Processes of refining aromatic hydrocarbons



Dec. 7, 1948.

P. J. WILSON, JR., ETAI- PROCESSES OF REFINING AROMATIC HYDROCARBONS Filed Sepjb. 11,' 1945 quality.

Patented Dec. 7, 1948 PROCESSES OF REFINING AROMATIC HYDROCARBQNS Philip J. wilson, Jr., Joseph n. weils, ena charles R. Liebel, Pittsburgh, Pa., assignors to Carmagie-Illinois Steel Corporation, a corporation of New Jersey Application september 11, 1945, serial No. 615,516

.a claims. (ci. 26o-674) Aromatic hydrocarbons ofthe type obtained from the light oil and tar produced in by-product coke plants, contain impurities which necessitate the rening of the hydrocarbons for adapting the said hydrocarbons to commercial use. Such impurities include paramnic, naphthenic, and sulphur compounds, together with unsaturated hydrocarbons. The `presence of such impurities prevents the hydrocarbons containing them from be- ,ing used in many industrial operations.,

Many processes have been devised for the removal of such impurities from the aromatic hydrocarbons, such removal being inexpedient by fractionation procedures owing to the closeness of the boiling points of the impurities. No complete analysis of the impurities present in benzol, toluol, or xylol, has ever been made, but some of the compounds have been identified and analyses made for their concentrations. Thus, in one nitration grade of benzene, the presence of one per cent impurities was found. Roughly onethird of thesevimpurities was found to be cyclohexane. Other naphthenic and parafflnic hydrocarbons boiling up to about 100 C. were present, but were not identified owing to analytical difculties. The total sulphur amounted to 0.05 per cent and included thiophene. Possibly carbon disulphide was present among the other sulphur compounds.

In another analysis of a benzol containing 0.5 per cent by volume of impurities, the impurities which were isolated distilled from 80 C. up to about 100 C. The greater portion, over 90 per cent, distilled above 90 C. The presence of 1y pentane, n-heptane, 1,1-dimethy1 cyclopentane E ily from the hydrocarbons, by further expedient 4 in the mixture was indicated by the boiling'v The presence of these impurities often is unde- I.

srable to consumers of the commercial products. In the first place, they represent a diluent of the benzol or the other aromatic hydrocarbons. In the second place, they give rise to undesirable side reactions in manufacturing processes which reduce the yield of nal product or affect its Thus the sulphur compounds have affected the color of dyes or the quality of pharmaceuticals in which benzol has been used. The yields of trinitrotoluene produced in the nitration of toluene is reduced by the presence of the tively in the industry.

The concentrations of the impurities have been reduced by various methods to which it is Superfluous to refer, these'being simple methods of separation, such as fractional distillation, which, however, is inexpedient because of the closeness of 'boiling points of the impurities to that of the hydrocarbon.

In accordance with the present invention there is provided a simple process for the substantially complete elimination of the impurities contained in the usual commercial grades of benzol, toluol, and xylol, the process of the invention being based upon a catalytic conversion of the impurities into compositions that may be removed readand known rening operations.

The process of the` present invention comprises contacting vapors of the hydrocarbon which is to be rened, with a combination of cracking and dehydrogenating catalysts at elevated vtemperatures. By the action of the catalysts, the impurities are broken down to lower molecular weight compounds, which can be removed more readily from the hydrocarbon after condensation of the catalytically-treated vapors by wellknown procedures, such as a combination of acid refining and distillation. i

By a cracking catalyst is meant one in which the principal reaction is a breaking of the bonds connecting carbon atoms in the molecule of a hydrocarbon, or between carbon and carbon, or carbon and sulphur in an organic sulphur comv v. l l h cyclohexane, methyl cyclohexane, 2,2,4-tri-methpound It may be illustrated for example by t e simple equation Y ciHm-i-(heat and catalyst) Cani-pcm@ By a dehydrogenating Acatalyst is meant one in whichV the principal reaction is a separation of hydrogen from the molecule. A reaction illustrating it is as follows:

hydrogenation. The chromic oxide may be sup` ported `onvthe silicate. thus' enabling the catais pumped by pump |02 through line |0 4provided with a control valve for controlling ilow of the hydrocarbon, for example, benzol, through pipe to catalyst chamber |I2, that contains a bed ||3 of the cracking catalyst, such as a silicate catalyst, which is in heat exchange relation with a heating fiuid maintained in the jacket 4, so that the catalyst chamber ||2` at a temperature ranging between about 250 C. to 500 C.

In the catalyst chamber ||2, there is effected a preliminary treatment of impurities present in the hydrocarbons by cracking such impurities as are amenable to such treatment. Carbon deposits 'on the catalyst bed and; as described above, lessen the activity of the catalyst. A pipe IIB connects to the bottom of catalyst chamber I |2, pipe ||8 being provided with a valve ||5 and opening into a stack not shown.

Connected to pipe i above the valve ||8 is a pipe |20, for transferring the initially treated hydrocarbon vapors to pipe |22 that enters the second catalyst chamber |24. The pipe is provided with valves and |21 for controlling flow of vapors therethrough. Pipe |22 has a valve Ill therein between pipe |20 and the catalyst `chamber |24.

The catalyst chamber |24 has a bed of dehydrogenating catalyst |28 therein, which bed may be a chromium oxide, for example. This system with inert gas, valve |40 is closed, and valve |42 is opened.

When the catalyst has been reviviiied as indicated by the absence of carbon dioxide in the gases exiting through pipes |22 and |50, valves |42, |48, |44. ||8, |45, and |50 are closed, and valves ||0, |25, |21, |3|, and |21 are opened for readmission of the hydrocarbon vapors to the system. However, after the carbon has been burned from the surface or the catalyst beds, it is important to fill the system again with inert gas as described above. Obviously, if needed, the air supply may be diluted with inert gas for controly ling the rate of combustion of the deposited carbed of catalyst |28 is heated to a temperature of from .500 C. to 600 C. by a heating fluid circulating through jacket |20 enclosing the chamber |24. The catalyst chamber |24 is the conversion environment for substantially all of theimpurities in the hydrocarbon vapors, such impurities being dehydrogenated into compounds that, together with the cracked compounds from cracking chamber H2, are removable readily from the condensate that is recovered from the dehydrogenation chamber |24.

For this purpose, a condenser |34 is provided, the condenser |34 being connected to the catalyst chamber |24 by a pipe |32. Outlet pipe |32 is provided with a valve |31.

As the vapors pass through the catalyst bed |28, carbon deposits on the catalyst and reduces the activity of the catalyst so that this carbon has to be removed from time to time, although this carbon deposit is not as heavy as that formed in chamber ||2.

The carbon deposited in both chambers I2 and |20 is removed conveniently by burning it off with air which is admitted periodically to both chambers ||2 and |24 during which periods the ow of hydrocarbon vapors to the system is interrupted.

For admission oi.' air, pipe |38 is provided', which is connected to a source of compressed air, and which connects with catalyst chambers ||2 and |24 through pipes Ill'and. |22 respectively. Since, however, the system will be filled with hydrocarbon vapors in order to avoid explosion, the pipe |38 is connected through pipe |40 to a source of inert gas such as steam or nitrogen. Pipe |38 is provided with a valve |42 between pipe |40 and the source of air, and pipes and |22 are provided respectively, with valves |44 and |46 between the pipes and I2 and the connections therewith of the hydrocarbon vapor lines. Pipe |40 is provided by a valve |48.

In order to regenerate the catalyst, valves |I0, |25, |21. |31 and |42 are closed, and valves |48, |44, I 8, |45, |3| and |50 are opened until the system is flooded with inert gas. After' iilling the bon, for preventing excessive rise in temperature in the catalyst beds.

The condensate collected in receiver |38 is ready for further rening.

The two catalyst chambers ||2 and |24 are heated by a hot iiuid circulating around them. Such iluid may be hot combustion gases from burning coke-oven gas, or any other available gaseous material heated suiilciently high to raise the catalyst chambers |24 and ||2 suiliciently highl to bring about the desired reactions. Charnber |24 is substantially hotter than is chamber ||2, as previously mentioned. However, a fused salt bath may be employed as `the heating medium, or the catalyst chambers may be heated electrically. When a hot gaseous heating medium is employed, it may be introduced through pipe |54 into jacket |30 enclosing catalyst chamber |24, and then vthrough pipe |58 into jacket ||4 around the catalyst chamber ||2, and out through outlet |58 to a stack, not shown.

We claim:

l. The process of purifying aromatic hydrocarbons containing not more than approximately ve per cent of impurities including paraiiinic, naphthenic, and sulphur compounds together with, possibly, unsaturated hydrocarbons, which comprises passing the hydrocarbon to be puriiied through successive catalytic environments, one of which contains a dehydrogenating catalyst and another contains a cracking catalyst, maintaining dehydrogenating catalyst at a temperature of from approximately 500 C. to approximately 540 C. and at substantially atmospheric pressure, with the cracking catalyst maintained at a temperature of from approximately 250 C. to approximately 500 C. and at substantially atmospheric pressure, thereby converting the said impurities into a condition readily removable from thearomatic hydrocarbon while leaving the aromatic hydrocarbon substantially unaffected.

2. The process of purifying an aromatic hydrocarbon of the group consisting of benzol, toluol, and xylol, obtained from light oil produced in the by-product cokingof bituminous coal, the said hydrocarbon containing not more than approximately five per cent of impurities including parafiinic, naphthenic, and sulphur compounds,

. together with, possibly, unsaturated hydrocarcondensate of aromatic hydrocarbon, for removing the said impurities therefrom.

3. The process of purifying aromatic hydrocarbons containing not more than approximately ve per cent of impurities including paranlc. napththenic, and sulphur compounds together with, possibly, unsaturated hydrocarbons, which comprises passing the hydrocarbon to be puried through successive catalytic environments,

one of which contains chromic oxide as a dehy- 1 drogenating catalyst and another of which contains a silicate as a cracking catalyst, maintaining the chromic oxide catalyst at a temperature of from approximately 500 C. to approximately 540 C. and at substantially atmospheric pressure, with the silicate catalyst being maintained at a temperature of from approximately 250 C. to approximately 500 C. and at substantially atmospheric pressure, thereby converting the said impurities into a condition readily removable from the aromatic hydrocarbon while leaving the aromaticv hydrocarbon substantially unaiected.

PHILIP J. WILSON, JR. JOSEPH H. WELLS. CHARLES R. LIEBEL.

. REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS 'dumber Name Date 266,187 sobe May 18, 1943 390,534 Pier et al May 18, 19,43

- 1,897,798 Guthke Feb. 14, 1933 1,932,365 Krauch et al Oct. 24, 1933 2,249,337 Visser et al July 15, 1941 2,380,279 lWelty July 10, 1945 2,404,902 Claussen et al July 30, 1946 

